Landscape-driven effects on taxonomic,functional, and phylogenetic diversity of vegetation developing on sand-gravel pits of early successional stages

Among the key drivers of the progressive transformation of biomes are mining activities, usually leading to the establishment of novel ecosystems, characterized by new species assemblages, combinations of habitats, and unprecedented functioning. It remains unknown how the composition of surrounding land cover may influence species composition, community assembly processes, and the phylogenetic relatedness structure of vegetation developing spontaneously on these de novo established biological systems. In this study, I investigated the influence of different landscape types in the proximity of 31 sand-gravel pits of pioneer successional stages on vegetation's taxonomical, functional, and phylogenetic diversity. Further, I accounted for the effects of the surrounding landscape on ten ecological groups of plant species, and biotic novelty indices as a supporting explanation of mechanisms shaping the species' co-occurrence patterns. I explored that plants' functional and phylogenetic diversity was higher in pits surrounded by riverine landscape, and lower if the contribution of settlements in the surrounding landscape was higher. Both landscape features promoted the occurrence of exotic species on sand-gravel pits, but only the settlements' proportion exerted a positive effect on biotic novelty indices. On the other hand, pits with a prevalence of forests in the surroundings were dominated by phylogenetically diverse, but functionally more homogenous native taxa, reflected, inter alia, in negative effects of forests on biotic novelty indices. Comprehensive assessment of the impacts of the surrounding landscape on different components of plant diversity may be used as a useful predictor in the exploration of successional trajectories, as well as a helpful tool in the formulation of strategies for mining-transformed ecosystems management.     

Basisphenoid and basioccipital pits in microchiropteran bats

We examined 686 skulls of 420 species of microchiropteran bats in 16 families to assess variation in pits in the basisphenoid and basioccipital bones. A total of 26 measurements were used to describe variation in pits, and patterns in the distribution of pits were examined across the families. Pits were absent from 154 species and present in 266 species. While some species had as many as four basisphenoid pits, basioccipital pits, when present, always occurred as a single pair. No species had more than four pits (basisphenoid or basioccipital and basisphenoid) in total. In some families all species either had pits (e.g. Emballonuridae) or none had pits (e.g. Rhinolophidae), but the incidence of pits usually was variable within families. The results of a cluster analysis of families based on the incidence of pits and morphological features of pits bore little resemblance to a recent phylogeny of Microchiroptera. A discriminant function analysis of features of pits of Emballonuridae, Phyllostomidae, Vespertilionidae and Molossidae correctly classified 66% of species to family revealing some continuity in pit structure among related species. There was no evidence of significant sexual dimorphism in the incidence or features of pits. Basisphenoid and basioccipital pits tended to increase in size with skull size. Neither the incidence nor the morphology of basisphenoid nor basioccipital pits was consistently associated with echolocation, diet or foraging behaviour. Pits were present or absent from species using either high‐intensity or low‐intensity echolocation calls, and the same was true of bats using high or low duty cycle modes of echolocation. Furthermore, the presence or absence of pits did not correspond to the presence or absence of harmonics in echolocation calls. We propose that basisphenoid and basioccipital pits are oscillators in the vocal tract and contribute to the production of non‐linear phenomena in vocalizations made by bats. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78 , 215–233.     

Robust Prediction of Treefall Pit and Mound Sizes from Tree Size Across 10 Forest Blowdowns in Eastern North America

Treefall pits and mounds, formed when trees are uprooted by wind, influence an exceptionally broad range of phenomena in forests, having impacts on vegetation composition, soil formation, erosion, and soil respiration, among other processes. For example, treefall pits and mounds are known to have plant species composition with more pioneer species than nearby undisturbed soil; these microsites also are wetter (pits) or drier (mounds) than undisturbed soil; and have lower rates of soil respiration. Therefore, knowledge of the extent or coverage of these microsites will improve estimates of several processes as well as vegetation composition at the stand and landscape scale. Such information would be timely, given predictions of climate-change driven increases in severe weather that is the primary agent of pit and mound formation. However, to date, there have been no attempts to define a robust relationship to predict the sizes of these microsites across multiple forest types in eastern North America. Here, we summarize field measurement of the relationship between tree size and treefall pit and mound sizes, across ten catastrophic windthrow study sites. We find that for all ten sites pooled, simple ln–ln regression explains almost 54% of the variation in sizes of treefall pits (n = 1,039) and treefall mounds (n = 962) on the basis of tree diameter. This relationship spans numerous soil types, 31 tree species, and tree sizes ranging from 5 cm to greater than 105 cm diameter. Such a relationship may be coupled with information on the severity of disturbance (for example, proportion of stems uprooted) and pre-disturbance tree size structure, to provide a basis for predicting the area covered by pit and mound microsites at the landscape scale, and thereby a basis to frame expected impacts on soil formation, carbon cycling, vegetation establishment, and other ecological, edaphic, and biogeochemical processes.     

Contrasting Patterns in Solitary and Eusocial Bees While Responding to Landscape Features in the Brazilian Cerrado: a Multiscaled Perspective

Landscape structure is an important determinant of biological fluxes and species composition, but species do not respond equally to landscape features or spatial extents. Evaluating “multi-scale” responses of species to landscape structure is an important framework to be considered, allowing insights about habitat requirements for different groups. We evaluated the response of Brazilian Cerrado’s bees (eusocial vs. solitary ones) to both the amount and isolation of remnant vegetation in eight nested multiple-local scales. Response variables included abundance, observed, and estimated species richness, and beta diversity (split into nestedness and turnover resultant dissimilarities). Eusocial species’ abundance responded to landscape structure at narrow scales of fragment isolation (250 m of radius from sampling sites), while solitary species’ abundance responded to broader scales to fragment area (2000 m). Eusocial species nestedness also responded to landscape features in broader scales (1500 m), especially to increasing fragment isolation. However, all the remaining response variables did not respond to any other landscape variables in any spatial scale considered. Such contrasting responses of the abundances of eusocial vs. solitary species are related to the inherent life-history traits of each group. Important attributes in this context are different requirements on food resources, population features, and flight abilities. Species-specific dispersal abilities may be the main determinants of the nested patterns found for eusocial species at 1500 m. Considering these results, we suggest that different bee groups are considered separately in further landscape analyses, especially in other Brazilian biomes, for a better understanding of landscape effects on these organisms.     

Biodiversity in agricultural landscapes: the ground beetle communities of woody uncultivated habitats

Agricultural landscapes can be defined as mosaics of landscape elements which are affected by farming practices. Woodland habitats, even though they are managed, are amongst the most stable elements of agricultural landscapes and can play a key role in the maintenance of biodiversity. This study of the ground beetle (carabid) communities of woodlands and woody linear features in a Scottish agricultural landscape shows that these habitats contribute significantly to the overall landscape diversity of these beetles. Communities in woods and hedgerows display the same species diversity and are both characterized by the presence of forest species. The main factors constraining carabid communities in both environments are the grazing intensity and, to a lesser extent, the type of soil. Heavily grazed locations are characterized by the occurrence of grassland species while forest species are restricted to ungrazed locations. At the landscape scale, the distribution of the forest species is limited by spatial isolation, indicating that there are insufficient functional links between woodland habitats in the study area. Isolation could be compensated for either by a better control of grazing so that linear features can be used as dispersal corridors for forest carabids or by planting more linear features and woods in the area.     

Wood anatomy of Gentianaceae, tribe Helieae, in relation to ecology, habit, systematics, and sample diameter

Twenty collections representing one species each ofSymbolanthus andTachia, and 17 species ofMacrocarpaea were studied by means of light microscopy and scanning electron microscopy (SEM). Wood details show that the three genera form a coherent group;Tachia differs from the others in only a few minor characters. Because the species studied form a natural group, wood variations within Helieae offer the basis for correlations and interpretations with respect to habit and ecology. Diameter of stems studied proves to be an important variable that must be taken into account. Correlations with stem diameter include wider vessels in outer wood of wider samples. This would correspond to deeper penetration of reliable water tables by roots of helioid trees or large shrubs. Ray height decreases with increase in stem diameter, an indication of paedomorphosis. Rays of all species are paedomorphic in histology by virtue of relative paucity or even absence of procumbent cells in multiseriate rays. Pseusoscalariform lateral wall pitting of vessels is also a feature characteristic of paedomorphosis. The assemblage of paedomorphic features correlates well with the conclusion, reached by authors who used cladistic methods, that Gentianaceae other than Gentianeae are derived from suffrutescent prennials. The Mesomorphy Ratio, which incorporates three vessel features, correlates with leaf length and with stem diameter. All Helieae are mesophytic, but to various degrees. Septate fiber-tracheids, where present, are typically near vessels and form a substitute for or an addendum to vasicentric axial parenchyma as a mechanism for photosynthate storage. Vestured pits occur on lateral wall pits of vessels of all Helieae, but not on the fibertracheids. Vestured pits show diversity withinMacrocarpaea, a feature of possible systematic significance.     

Biodiversity of soil macrofauna in the New Forest: a benchmark study across a national park landscape

The New Forest National Park is a hotspot for biodiversity in the UK. A long history of grazing by ponies in the New Forest landscape has created a diverse mosaic of habitats that are of international significance. We investigated patterns of species diversity and composition across the New Forest landscape by sampling soil, leaf litter and ground macrofauna from woodland, grassland and heathland plots across the entire landscape. We used a spatially replicated design of hand sorted soil pits, Winkler extraction of leaf litter, and pitfall traps. We concentrated on diversity patterns of the following target groups: Coleoptera, Formicidae, Isopoda, Chilopoda, Diplopoda, Opiliones and Lumbricidae. The most striking difference in species assemblages is between wooded and open areas. Woodlands are the most diverse habitats and have a distinct assemblage, largely due to those leaf litter invertebrate species which are only present under a closed canopy. Open areas are less diverse, with diversity particularly low in the wet grasslands. However, the open areas do have a distinct fauna, especially in the wet and dry heaths which are home to a number of rare species, particularly of Formicidae. We discuss the potential conservation problems facing the New Forest and how these might affect soil macrofauna biodiversity in the future and conclude that climate change; over-grazing; and land use changes represent the largest threats. Although a relatively stable landscape which benefits from protection under UK law, changes in grazing intensity or management practices in the New Forest, particularly for some of the habitats of European importance (e.g. wet heathlands), could negatively affect soil macrofauna biodiversity. Climate change may also exacerbate biodiversity decline as a result of increased grazing intensity or changes in management.     

梣属11种植物次生木质部附物纹孔的电镜观测

应用扫描电镜对梣属11种植物次生木质部导管附物纹孔的分布和形态进行了详细的观察,应用Carnoy2.0软件和扫描电子显微镜采集的照片,测定了附物纹孔丰富度指标和纹孔数量特征指标。电镜观察表明,梣属11种研究植物次生木质部导管分子侧壁附物纹孔的分布和形态变化较大,附物纹孔丰富度指标的统计描述进一步证实附物纹孔的分布变化大;3个附物纹孔丰富度指标分别与管间具缘纹孔数量特征指标的逐步回归分析表明,导管侧壁附物纹孔丰富度2个指标,即导管外纹孔口附物频率与导管纹孔腔附物频率随纹孔口面积百分比的增大而增大,推测梣属植物附物纹孔丰富度与纹孔几何构造及数量特征有关。研究认为,附物纹孔在梣属植物稳定存在,是可界定梣属植物的木材解剖性状。     

Algal flora of certain gravel pits in the Thames Valley,U.K.

Summary Detailed analyses are presented of the phytoplankton of two pairs of gravel pits in the Surrey-Middlesex area of the Thames Valley. One of each pair has been recently excavated while the other is much older.Gravel dredging was fairly localised during the investigation, so that it was possible to study an area of disturbed water and an area of undisturbed water in each pit.The distribution of the algae in general and the frequency of the principal members of the phytoplankton were correlated, as far as possible with the physical and chemical features of the environment.Certain algae were found to favour the new or alternatively the old pits and there was some indication that some of the algae recorded in larger numbers thrived best in the disturbed or otherwise the undisturbed water of a pit.The total number of species observed in the new pits was considerably smaller than that in the old pits. Estimates of the total phytoplankton indicates that the new pits are richer, but less varied than the old pits.All the pits were flooded once by Thames water during the course of the investigation. Reasons are given for concluding that this flooding did not cause undue contamination with river phytoplankton.     

Rolling pits of Hartmann’s mountain zebra (Zebra equus hartmannae) increase vegetation diversity and landscape heterogeneity in the Pre‐Namib

Microsites created by soil‐disturbing animals are important landscape elements in arid environments. In the Pre‐Namib, dust‐bathing behavior of the near‐endemic Hartmann''s mountain zebra creates unique rolling pits that persist in the landscape. However, the ecohydrological characteristics and the effects of those microsites on the vegetation and on organisms of higher trophic levels are still unknown. In our study, we characterized the soil grain size composition and infiltration properties of rolling pits and reference sites and recorded vegetation and arthropod assemblages during the rainy season of five consecutive years with different amounts of seasonal rainfall. We further used the excess green vegetation index derived from drone imagery to demonstrate the different green up and wilting of pits and references after a rainfall event. In contrast to the surrounding grassland, rolling pits had finer soil with higher nutrient content, collected runoff, showed a higher infiltration, and kept soil moisture longer. Vegetation in the rolling pits was denser, dominated by annual forbs and remained green for longer periods. The denser vegetation resulted in a slightly higher activity density of herbivorous arthropods, which in turn increased the activity density of omnivorous and predatory arthropods. In times of drought, the rolling pits could act as safe sites and refuges for forbs and arthropods. With their rolling pits, Hartmann''s mountain zebras act as ecosystem engineers, contributing to the diversity of forb communities and heterogeneity of the landscape in the Pre‐Namib.     

What the Penaeaceae alliance (Myrtales) tells us about the nature of vestured pits in xylem

Molecular studies indicate that Penaeaceae, Oliniaceae, and the monospecific families Alzateaceae and Rhynchocalycaceae form a clade of Myrtales. Of these four families, Penaeaceae have tracheids with vestured pits, whereas the others have septate fibers lacking vestures; all have vestured pits in vessels. Tracheid presence in Penaeaceae may be related to the arid South African habitats of the family. Presence of vestures on tracheids in families with vestured vessel pits is one indication that imperforate elements are tracheids and are conductive cells, whereas fiber-tracheids and libriform fibers are non-conductive. Tracheids occur widely in angiosperms and may be plesiomorphies or apomorphies. Combretaceae, the first branch of the Myrtales clade, has a great diversity of vesture features in vessels compared to the Penaeaceae alliance families. Alzatea has vestures that spread over the inside of the vessels, whereas in most taxa of the alliance, vestures are confined to the pit cavities and pit apertures. Vestures in the alliance tend to be globular in shape, and are bridged together by strands of wall material. Lignotubers and roots in Penaeaceae have vestures much like those in stems. Only a few species and genera (notably Alzatea) of the alliance have vesture features the pattern of which correlates with the current taxonomic system. Vestured pits should be viewed from the inside surface of vessels as well as the outer surface, and although sectional views of vestured pits are infrequent, they are very informative. Studies that explore diversity from one order or family to another are needed and offer opportunities for understanding the evolutionary significance of this feature.     

Individual dispersal,landscape connectivity and ecological networks

Connectivity is classically considered an emergent property of landscapes encapsulating individuals' flows across space. However, its operational use requires a precise understanding of why and how organisms disperse. Such movements, and hence landscape connectivity, will obviously vary according to both organism properties and landscape features. We review whether landscape connectivity estimates could gain in both precision and generality by incorporating three fundamental outcomes of dispersal theory. Firstly, dispersal is a multi‐causal process; its restriction to an ‘escape reaction’ to environmental unsuitability is an oversimplification, as dispersing individuals can leave excellent quality habitat patches or stay in poor‐quality habitats according to the relative costs and benefits of dispersal and philopatry. Secondly, species, populations and individuals do not always react similarly to those cues that trigger dispersal, which sometimes results in contrasting dispersal strategies. Finally, dispersal is a major component of fitness and is thus under strong selective pressures, which could generate rapid adaptations of dispersal strategies. Such evolutionary responses will entail spatiotemporal variation in landscape connectivity. We thus strongly recommend the use of genetic tools to: (i) assess gene flow intensity and direction among populations in a given landscape; and (ii) accurately estimate landscape features impacting gene flow, and hence landscape connectivity. Such approaches will provide the basic data for planning corridors or stepping stones aiming at (re)connecting local populations of a given species in a given landscape. This strategy is clearly species‐ and landscape‐specific. But we suggest that the ecological network in a given landscape could be designed by stacking up such linkages designed for several species living in different ecosystems. This procedure relies on the use of umbrella species that are representative of other species living in the same ecosystem.     

Can the invasive European rabbit (Oryctolagus cuniculus) assume the soil engineering role of locally-extinct natives?

Habitat modifying species can play crucial roles in ecosystem function. Invasive engineers may assume these roles where native engineers have been lost from the system. We compared the dynamics of the foraging pits of an invasive engineer, the European rabbit (Oryctolagus cuniculus) with two native mammals, the greater bilby (Macrotis lagotis) and the burrowing bettong (Bettongia lesueur). Foraging pits are small surface depressions created by animals when they forage for seeds, bulbs, roots, invertebrates and fungi. We measured foraging pit density and turnover, and density and richness of plant seedlings in pits and adjacent surfaces across three landforms representing a gradient in resource availability inside (bilbies and bettongs), and outside (rabbits only) a reserve in an arid Australian shrubland over 2 years. Pits of the native engineers contained 80% more seedlings (11.2 plants m⁻²) than rabbit pits (6.22 plants m⁻²). Further, rabbit pits supported 3.6-times fewer seedlings than equivalent non-pit surfaces outside the exclosure. Only one plant species was restricted entirely to pits. The reserve had more foraging pits and greater turnover than outside, but contrary to prediction, pit effects on seedling density were no greater in the more resource-limited dunes. There were some strong temporal and landscape effects on pit density and species composition, but generally trends were similar inside and outside the reserve. Overall, despite their functional similarities, invasive rabbits created fewer pits that were less favourable patches for seedlings than those of native engineers. Our work suggests that a suite of ecosystem processes associated with fertile patch creation has potentially been lost with the extirpation of bilbies and bettongs.     

Can postmining revegetation create habitat for a threatened mammal?

Most revegetation conducted for biodiversity conservation aims to mimic reference ecosystems present predisturbance. However, revegetation can overshoot or undershoot targets, particularly in the early stages of a recovery process, resulting in conditions different from the reference model. Revegetation that has, as yet, failed to fully meet revegetation targets may, nonetheless, provide habitat for threatened species not present in reference ecosystems. To investigate this possibility, we surveyed Quokka (Setonix brachyurus), a threatened macropod, in a mining landscape in south‐western Australia. We established four sites in each of riparian forest, which is the preferred habitat of quokkas but is not mined, mid‐slope forest, which is the premining reference ecosystem but is not suitable habitat for quokkas, and revegetated forest on mine pits 16–21 years postmining. We recorded quokkas in all riparian forest sites and two revegetated forest sites but not in any mid‐slope forest sites. Occupied revegetated sites had greater cover between 0 and 2 m and were spatially closer to riparian forest than unoccupied revegetated sites, suggesting predation pressure was likely influencing which mine pits were occupied. Our study demonstrated postmining revegetation can provide new habitat for a threatened species and suggested that revegetating a small proportion of sites to provide new habitat for threatened species could be considered as a management option in some scenarios. This could improve landscape connectivity and increase both the area of available habitat and between‐site heterogeneity, which could all potentially increase the ability of revegetation to conserve biodiversity.     

Spontaneous Vegetation Succession in Gravel–Sand Pits: A Potential for Restoration

Vegetation variability, the participation of target and undesirable species, and the role of local species pool were studied in the course of spontaneous succession in disused gravel–sand pits. The study was conducted in various regions of the Czech Republic, Central Europe. The regions represented either agrarian lowlands with a relatively warm and dry climate or mostly woodland uplands with a relatively cold and wet climate. The gravel–sand pits (36) comprised stages of different age from 1 to 75 years since abandonment. Altogether, 224 vegetation samples were recorded with species cover (%) visually estimated. Species affinity to different vegetation types was assessed in each sample based on the species cover. Local site factors, such as water table and soil characteristics, and landscape characteristics, namely climatic parameters, presence of nearby (semi)natural plant communities and main land cover categories in the broader surroundings, were evaluated as well as the participation of target (grassland, woodland, and wetland) and undesirable (ruderal, alien) species. Ordination analyses showed that vegetation succession led to target grassland, wetland, or woodland vegetation depending on local site factors, especially moisture and the presence of (semi)natural vegetation in the surroundings (local species pool). Restoration of target vegetation in disused gravel–sand pits by processes of spontaneous succession can be possible and successful in about 25 years, especially if (semi)natural vegetation exists in the surroundings. The invasion of the alien tree Robinia pseudacacia must be taken into consideration within the dry sites in lowlands.     

Quantifying spatial classification uncertainties of the historical Wisconsin landscape (USA)

Landscape feature can be classified by creating categories based on aggregation of spatially explicit information. However, many landscape features appear continuous rather than discrete. The aggregation process likely involves loss of information and introduces a variety of uncertainties whose degree and extent may differ spatially. Since landscape classifications have found wide application in e.g. natural resource policies or ecological research, assessments of spatial classification uncertainties are required.
We present a quantitative framework to identify the degree of landscape continuity (fuzziness) and structure (categorization) based on fuzzy classification and offer measures to quantify uncertainties originating from aggregating features into categories. Fuzzy classification is a non-hierarchical, quantitative method of assessing class definitions using degrees of association between features and class. This results in classes which are well defined and compositionally distinct, as well as classes which are less clearly defined but which, to various degrees, share characteristics with some or all classes. The spatial variation in the degree of class definition on the landscape is used to assess classification uncertainties. The two aspects of uncertainty investigated are the degree of association of a feature with the overall class definitions (membership diffusion), and the class-specific degree of association of each pixel on the landscape with each class (membership saturation).
Three classification scenarios, one fuzzy and one discrete, of the historical landscape of Wisconsin (USA) were compared for spatial classification uncertainties. Membership diffusion is highest in topographically heterogeneous environments, or areas characterized by many species occupying similar ecological niches. Classification uncertainties for individual classes show that differentiated species distributions can be identified, not only distribution centers.     

Ecosystem Management of Desertified Shrublands in Israel

The objectives of this study were to understand the ecological processes and possible management strategies in desertified shrublands. We hypothesized that biological production and diversity in desertified shrublands in the Negev in Israel are low due to water, soil, and nutrient leakage from the ecosystem. We designed a series of field experiments in order to examine (a) whether source–sink relationships exist between the crusted soil and the shrub patches, (b) whether resources (water, soil, and nutrients) leak from the system, and (c) whether management, which changes the landscape mosaic by introducing new sink patches that reduce leakage of resources, may increase productivity and diversity. The results indicate that the low number of shrub patches, which serve as sinks for resources, leads to water, soil, and nutrient leakage from the ecosystem. This leakage reduces ecosystem production and diversity. We found that artificially created pits, which act as sinks for resources, decrease leakage and increase biomass production and annual plant species diversity. Based on the experimental results, we developed conceptual models for shrubland desertification and ecosystem management. The models are based on a source–sink relationship between two patch types characteristic of shrublands. The models relate landscape productivity to the number of sink patches and suggest that, in cases where there are too few sinks, artificially created sink patches should be added. Management methods were developed to reduce resource leakage in the desertified shrubland of the Negev. Methods included construction of man-made pits in the landscape that add resource-enriched patches to the landscape. These patches are used to create parks consisting of clusters of trees integrated into a matrix of shrubs and herbaceous vegetation. The managed parks are used for recreational purposes and for rangeland. Received 8 July 1997; accepted 7 July 1998.     

Genetic effects of landscape,habitat preference and demography on three co‐occurring turtle species

Expanding the scope of landscape genetics beyond the level of single species can help to reveal how species traits influence responses to environmental change. Multispecies studies are particularly valuable in highly threatened taxa, such as turtles, in which the impacts of anthropogenic change are strongly influenced by interspecific differences in life history strategies, habitat preferences and mobility. We sampled approximately 1500 individuals of three co‐occurring turtle species across a gradient of habitat change (including varying loss of wetlands and agricultural conversion of upland habitats) in the Midwestern USA. We used genetic clustering and multiple regression methods to identify associations between genetic structure and permanent landscape features, past landscape composition and landscape change in each species. Two aquatic generalists (the painted turtle, Chrysemys picta, and the snapping turtle Chelydra serpentina) both exhibited population genetic structure consistent with isolation by distance, modulated by aquatic landscape features. Genetic divergence for the more terrestrial Blanding's turtle (Emydoidea blandingii), on the other hand, was not strongly associated with geographic distance or aquatic features, and Bayesian clustering analysis indicated that many Emydoidea populations were genetically isolated. Despite long generation times, all three species exhibited associations between genetic structure and postsettlement habitat change, indicating that long generation times may not be sufficient to delay genetic drift resulting from recent habitat fragmentation. The concordances in genetic structure observed between aquatic species, as well as isolation in the endangered, long‐lived Emydoidea, reinforce the need to consider both landscape composition and demographic factors in assessing differential responses to habitat change in co‐occurring species.     

TRACHEID BAR AND VESTURED PITS IN LEGUME SEEDS (LEGUMINOSAE: PAPILIONOIDEAE)

The tracheid bar, a strip composed of vertically oriented large tracheid-like cells (tracheoids), occurs only in the hilum of seeds of papilionoid legumes. An anatomical survey of the bar was made from seeds representing 232 species of 97 genera from 29 of the 31 tribes recognized by Polhill. Seeds were sectioned freehand, coated, then viewed by SEM. The tracheid bar is quite uniform in its general features throughout the subfamily, although differences in size and shape of both the bar and the tracheoids were found. Eight species from tribes considered to be among the primitive elements of the subfamily exhibited three variant forms: horizontal tracheary elements instead of the usual bar (2 species), tracheid bar with subtending but separate vascular bundle (1 species), and the tracheid bar with fused horizontal tracheary elements (5 species). Bordered pits of individual cells in the tracheid bar virtually always lacked a membrane and had smooth, warty, or variously elaborate vestures on the border. This appears to be the first report of vestured pits other than in secondary xylem. With some exceptions, bordered pits tended to be vestured in primitive tribes, warty in intermediate tribes, and smooth or only slightly warty in the most advanced tribes.     

Effects of stone topography on abundance of net-building caddisfly larvae and arthropod diversity in an upland stream

We investigated whether small pits on the surfaces of stream stones affected abundances of net-spinning, hydropsychid larvae (Trichoptera) and species diversity in the Acheron River, southeastern Australia. On stream stones, nets occurred more often in small (at least 5 mm width) pits than expected by chance. However, proportionately high numbers of pits were not associated with high abundances of either of two species of hydropsychid larvae (both Asmicridea spp). A colonization experiment, using bricks with 0, 4, 12 or 30 small (diam. 5.5 mm) and large (13 mm) pits drilled into the top surfaces, showed that numbers of nets were related to numbers of pits. Small pits were preferred over large ones and the pits, as a group, were occupied almost entirely by late instars of both species. However, only Asmicridea sp. 1 was more abundant on pitted bricks; Asmicridea sp. 2 showed no response. The differences between the species, and between the stone and brick results, can be explained by different proportions of late instars in the samples. Many I instars probably did not make nets. Hence, higher numbers of larvae on pitted surfaces is expected only when late instars are relatively frequent, as was true for Asmicridea sp. 1 on bricks. There were no effects of pits per se or increased numbers of hydropsychid nets on species diversity or the abundances of other common species. These results contrast with those of other studies, which found stone topography or hydropsychid nets to increase species diversity on stones.